The present invention relates to a driving mechanism used to precisely drive a driven object using a driving means, such as a stacked piezoelectric actuator, and more particularly to an optical-element driving mechanism used to drive an optical element in a desired direction or to deform an optical element, such as a lens and a mirror, so as to obtain a more precise imaging relationship in exposing an image of a reticle (mask) onto a substrate (silicon wafer). The optical element described in the embodiments will cover a lens, a parallel plate glass, a prism, a mirror, and a diffraction optical element, such as a binary optics.
A semiconductor exposure apparatus used for a lithography process in manufacturing semiconductor devices and micro devices is an apparatus that transfers onto a substrate an original having various different types of patterns. The integrality of the semiconductor device increases year by year: In order to produce a circuit pattern with this high integrality, an aberration and distortion of a projection optical system need to be reduced.
An optical-element driving method is one method for reducing the aberration and the distortion of the projection optical system, and displaces an optical element in the projection optical system in the optical-axis direction or tilts the optical element. This method provides at least five optical-element driving units in the projection optical system, and adjusts an optical error component, a spherical aberration, a coma, a magnification error, a curvature of field, and a distortion caused by ambient changes (such as pressure and temperature variances), a variation with time, and an exposure heat. An optical-element deforming method is another method, and deforms (or corrects) a surface shape of an optical element. In this case, an optical-element driving unit adjusts a self-weight deformation of the optical element's surface that occurs in supporting or holding the optical element, or reduces the exposure aberration that occurs with a specific illumination mode.
Prior art disclose the following optical-element driving mechanism or method for a semiconductor exposure apparatus:
FIG. 2 of Japanese Patent Laid-Open No. (“JP”) 2001-343575 shows an outer ring corresponding to a lens barrel, and an inner ring corresponding to a movable ring frame. That figure also shows three optical-element holding units corresponding to a lens driving mechanism arranged at angles of 120° on the outer ring, and a connecting arm that serves as an output displacement part of the driving mechanism and is coupled with the inner ring. Control over three output displacements of the driving mechanisms to desired values can shift the movable lens in the optical-axis direction, and tilt the movable lens around two axes orthogonal to the optical axis. FIGS. 12 and 13 show a detailed structure and an optional principle diagram of the driving mechanism. These figures show a mechanism that uses a piezoelectric element as a driving source, and an elastic hinge mechanism that includes a rigid link and an elastic hinge and has a displacement enlargement and guide functions, to drive the connecting arm coupled with the movable lens, in the optical-axis direction of the lens.
Prior art also disclose the following apparatus (or optical-element deforming method) that controls a surface shape of the optical element:
JP 2000-195788 discloses, in its FIG. 1, an optical-element surface-shape controlling apparatus that includes plural actuator pairs arranged in the radial direction, and a transmission that converts the actuator's power into a displacement in the optical-axis direction. In that figure, four actuators and the transmissions are arranged at regular intervals around the optical axis so that mutually facing driving parts can push or draw each other.
However, the above prior art has the following defects:
The driving mechanism disclosed in JP 2001-343575 arranges the actuator and the elastic hinge mechanism in the optical-axis direction of the lens in parallel, and thus requires such a thick outer ring corresponding to the lens barrel that it is difficult to house a mechanism in a lens unit that is thin in the optical-axis direction. The lens unit mounted with the mechanism is limited to a thick unit in the optical-axis direction, restricting the degree of freedom of the optimal reduction of the aberration of the entire projection optical system.
There is another problem: When a small generation displacement of an input source is amplified so as to obtain a large lens driving range, it is likely that the natural frequency of the system lowers, and the external vibration given to the barrel transmits to the lens. Thus, for a high imaging performance, it is difficult to use a highly sensitive lens, and a lens that requires high speed driving.
There is still another problem: The power by a driving source deforms the barrel, and displaces a sensor attachment part that measures a movable-part position. As a result, it is difficult to maintain a desired positional accuracy.
JP 2000-195788 discloses only a conceptual diagram, rather than a concrete structure, of a power-displacement converting transmission that converts the tensile force and/or the compressive force of plural actuators that are arranged in the radial direction. This structure, if viable as a unit, provides a rotational action around a pivot as well as the optical-axis direction. For example, the rotational action around a right end 12 in FIG. 2, the internal ring (2) is subject to an unintentional deformation and a precise adjustment of the optical performance becomes difficult.